Drill bits are well known devices for cutting or boring holes in a wide variety of materials. The well known twist drill bit and the helical shaft auger type bit both have one or more cutting edges mounted on one end of an elongated cylindrical shaft of uniform diameter. The elongated shaft maintains the orientation of the cutting edges in the hole produced to generate a straight bore. Once the twist or helical auger drill bit completes cutting the hole, it is easily withdrawn because the elongated cylindrical shaft in contact with the interior surface of the bore guides the drill bit removal therefrom.
Another variety of drill bit is available for cutting holes in materials, including sheet material up to several inches thick. This variety is called a hole bit, a hole boring tool, a Forstner bit, or a Selfeed bit. The hole bit has one or more cutting edges on one end of a relatively short cylinder with an opening ahead of the cutting edge to remove cutting chips. A shank or shaft of smaller diameter than the short cylinder is fastened opposite the cutting edges for attachment to the chuck of a drill. Hole bits are available having a cylinder diameter up to about 6 inches and even larger. The hole bits also may employ cutting teeth around the circumference of the cutting cylinder in addition to the cutting edges on the face of the cylinder. In addition, a penetrating spike in the center of the cutting face may be present to hold the hole bit at a specific location during the cutting of a hole.
The hole saw cutting tool is similar in construction to the hole bit. The hole saw has no cutting edges on the cylinder end. The saw tool has only cutting teeth around the circumference of the cutting cylinder and a penetrating spike in the center of the cutting face to hold the hole saw at a specific location during the cutting or sawing of a hole. The hole saw cutting tool has no opening to remove the cut out plug from the produced hole, and thus the saw tool is generally limited to use on sheet material work pieces up to several inches thick. Examples of both the hole bit and the hole saw are shown in FIG. 1 and FIG. 8, respectively.
When using the above-described hole bit or hole saw for cutting holes in materials, including sheet material up to several inches thick, withdrawal of the hole bit or hole saw from the cut hole can be difficult, particularly for a larger diameter hole bit or hole saw. Once the short cylindrical cutting portion of the tool moves through the cut hole, the operator must perfectly align the cutting cylinder in the cut hole to withdraw the hole bit or hole saw. This is time consuming and impedes the cutting of multiple holes as may be needed in a production facility.
Some examples of innovative devices used for drilling or cutting holes are disclosed by the following patents. Harding, in U.S. Pat. No. 2,344,143, discloses a twist drill bit fitted with a countersink and depth gauge. Moore et al., in U.S. Pat. No. 3,182,531, describe a reamer of uniform diameter. In U.S. Pat. No. 3,199,382, Andreasson discloses a drill bit with a hollow shank for cooling fluid, and a reaming insert of hard material. The whole device is of essentially uniform diameter.
In U.S. Pat. No. 3,778,180, Ostrom discloses a twist drill with a larger diameter shank for use in drilling printed circuit boards. Tanner et al., in U.S. Pat. No. 3,806,270, describe a fluted twist drill bit with a head part of greater diameter than the body part. The drill bit fits into a tubular drill stem that delivers a fluid for flushing away cuttings from the hole. U.S. Pat. No. 3,945,753 by Byers et al. discloses a drill bit with detachable blades and shank, the shank having a much smaller diameter than the diameter of the drill bit.
Walton, II, in U.S. Pat. No. 4,239,427, and Timmons, in U.S. Pat. No. 4,244,667, disclose a boring tool with several small triangular shaped supports between a circular drill bit and a connecting holder for the drill bit shank. In U.S. Pat. No. 5,092,719, Zsiger describes a drilling/cutting tool with a single or double spiral shank to assist in removal of chips during the cutting/drilling process. The spiral shank is decidedly smaller than the diameter of the hole produced.
In U.S. Pat. No. 3,645,642, Koslow describes a drill bit with a twist bit cutting end that has a progressively increasing diameter extending from a cutting end of small diameter to a rearward section of largest diameter, then tapering to a shank section of smaller diameter. The tapered drill bit prevents binding when drilling deep holes. In U.S. Pat. No. 4,189,266, Koslow describes a four-fluted tapered drill bit having a cutting section of increasing diameter connected to a section of decreasing diameter. This is connected to a shank for mounting the bit in a power drill.
Applicant has invented a device which easily guides a hole bit or a hole saw back though a cut aperture in a work piece of any thickness.